CN108778663A - The method for forming product - Google Patents

Abstract

The present invention provides the methods for forming product by the molten plastic composition comprising polymer and foaming agent.This method includes injecting the molten plastic composition in mold, so that the plastics composite forms the first solid surface layer that is adjacent with the first formation chamber surfaces of mold and contacting, the second solid surface layer that is adjacent with the second of mold the formation chamber surfaces and contacting, before molten plastic composition solidification between the first and second solid surface layers in at least part of neighboring area of mold of limit chamber annular cross section, the mold is opened.

Description

method of forming an article

The present invention relates to forming expanded plastic articles such as cups or containers for food.

In the packaging industry, a common type of disposable cup, such as a takeaway coffee cup, is a paper cup with an inner liner of plastic material such as low density polyethylene (LDPE). Because these cups are made of two different materials, their separation can be difficult and/or expensive, and their recycling can therefore prove a challenge. Furthermore, because there is a seam on one side of the cup (where the paper material is bonded together), when the cup is tilted for consumption of said beverage therein (especially when the cup is used to connect to a lid with the beverage passing through it through the mouthpiece used for consumption), the liquid will leak from the joint area at the rim of the cup.

Efforts have been made in the industry to provide disposable polypropylene cups. For example US-A-2014/0166738 discloses a blank made of a porous polymer material such as polypropylene which can then be formed into a cup. But there is still a seam in the cup of US-A-2014/0166738 and the final cup has to be manufactured by folding the blank and sealing its different edges together. Also, in conventional injection molding, thick walls are required to create some insulation in the cup. Typically, the porous structure provides thermal insulation, and blowing agents are added to the thermoplastic polymer to create a foamed structure, to further improve thermal insulation, and to reduce the density of the foamed walls. However, for a given wall thickness, the maximum density reduction that can be achieved by foaming is 30 wt%, based on the weight of thermoplastic polymer in the wall.

It is an object of the present invention, at least in part, to overcome the problems of existing disposable containers. Specifically, there is a need in the art for containers that are easily recyclable. It would also be desirable to reduce the amount of material used to manufacture each container while still providing containers with good thermal insulation and desired levels of stiffness.

In a first aspect, the present invention provides a method of forming an article, the method comprising:

(a) providing a mold having an outer part having a first cavity-forming surface and an inner part having a second cavity-forming surface;

(b) closing the mold thereby defining a cavity between the first and second cavity-forming surfaces, wherein at least one region of the cavity defines the cavity between the outer and inner peripheral edges of the cavity An annular cross-section, the first forming chamber surface is such that the distance between the first forming chamber surface and the second forming chamber surface alternates between a first distance and a second distance around at least part of the perimeter of the region , the first distance is greater than the second distance;

(c) injecting a molten plastic composition comprising a polymer and a blowing agent into the cavity;

(d) causing the plastic composition to form a first solid skin and a second solid skin in the at least one region, the first solid skin being adjacent to and in contact with the first forming chamber surface, and having a first perimeter length , the second solid skin is adjacent to and in contact with the second forming chamber surface, and has a second perimeter length, wherein the plastic composition remains molten between the first and second solid skins to form, respectively: wherein the The distance between the first forming chamber surface and the second forming chamber surface alternates between the first distance and the second distance, alternating the first and second thicknesses of the plastic composition, the first and second thicknesses each comprising first and second skins and a molten plastic composition therebetween;

(e) before the plastic composition between the first and second solid skins solidifies, the mold is opened, thereby allowing the plastic composition between the first and second solid skins, and the plastic composition to alternate molten plastic compositions of first and second thicknesses, expanded by foaming, wherein said opening comprises removing the outer part of the mold such that the first solid skin no longer contacts the first forming chamber surface, Instead, the second solid skin remains in contact with the second forming chamber surface.

The second solid skin may remain in contact with the second forming chamber surface until the plastic composition between the first and second solid skins is fully expanded.

The first and second distances and corresponding first and second thicknesses are configured to provide a series of alternating peaks and grooves, or ridges and valleys, around the perimeter of the injected composition. These values may be constant or alternatively both the first and second distances and thickness may vary independently around the perimeter. In some embodiments of the invention, the first and second distance and thickness are constant around said perimeter. In other embodiments of the invention, the second distance/thickness is constant around said perimeter and the first distance/thickness varies around said perimeter. In other embodiments of the invention, the first distance/thickness is constant around said perimeter, and the second distance/thickness varies around said perimeter. In other embodiments of the invention, the second distance/thickness is a constant value around said perimeter, and the first distance/thickness alternates between two different first values around said perimeter. In other embodiments of the invention, both the first and second distance/thickness vary independently around said perimeter.

In a second aspect, the present invention provides a hollow article for use as a beverage cup or as a container, the hollow article having an annular side wall and a bottom wall defining a central hollow chamber, the top edge of the side wall and the The bottom end, wherein the annular side wall comprises a plastic material consisting of a sandwich of inner and outer skins and an expanded porous foam layer therebetween, wherein the expanded porous foam layer comprises an annular array of reinforced regions which extending longitudinally along the sidewall in a direction between the top edge and the bottom end, the reinforced region is passed through an annular array extending longitudinally along the sidewall in a direction between the top edge and the bottom end Spacer regions are spaced apart from each other to provide alternating reinforcement regions and spacer regions around the annular sidewall, wherein the reinforcement regions comprise expanded first density cellular foam and the spacer regions comprise expanded second density cellular foam, wherein the The first density is higher than the second density.

Preferred features of each aspect are defined in the respective dependent claims.

An advantage of the present invention is that the container formed by its method is easily recycled and reused, it has no such joints in the material through which leakage of the liquid contained therein can occur, it has the required strength degree level, and also has good thermal insulation. Furthermore, the present invention allows the use of less material to manufacture each container (thus reducing manufacturing costs).

Using the present invention, a 200% drop in density between the density of the thermoplastic resin in its unfoamed state and the density of the thermoplastic material in the cup, which includes expanded cellular foam regions and unfoamed regions, can be achieved.

The present invention is based at least in part on the inventors' discovery that a first forming chamber surface is provided such that the distance between the first forming chamber surface and the second forming chamber surface is between the first distance and Alternating between second distances (the first distance being greater than the second distance) allows reducing the amount of material used to form the article and thus also reducing the weight of the article. Specifically, in a first aspect, the inventors have discovered that the first solid skin (formed before the mold is opened) can be opened when the mold is opened (the mold is opened before the molten plastic composition between the first and second skins solidifies) ) "blown up" by foaming the molten plastic composition. The distance between the first and second solid skin layers of the final article may be substantially constant around the perimeter of the final article. Therefore, the method of the present invention uses less material, but provides such a final product, its appearance is similar to the distance between the first forming cavity surface and the second forming cavity surface in the mold is kept constant, while Not the product obtained by alternating between the first and second distances.

In a second aspect, the inventors have found that when forming the final container (wherein some regions comprise expanded plastic composition and some regions comprise unexpanded plastic composition), providing a first cavity-forming surface is such that the first The distance between a forming cavity surface and the second forming cavity surface alternates between a first distance and a second distance around at least a first portion of the area perimeter (the first portion being the area which when opening the mold expansion), which makes it possible to reduce the amount of material used to form the product, and thus reduce the weight of the product. Specifically, the first solid skin in the first part (formed before opening the mold) can be "blown" by foaming the molten plastic composition between the first and second skins in the first part, so that The first skin is the convexity in the first part of the final article. Therefore, the method of the present invention uses less material, but provides such a final product, its appearance is similar to the distance between the first forming cavity surface and the second forming cavity surface in the mold is kept constant, while Not the product obtained by alternating between the first and second distances.

The present inventors have also found that articles produced by the method of the present invention also have the desired level of stiffness for such articles, albeit with reduced amounts of material used therein. It has also been found that on slow cooling of a cellular foamed plastic composition, typically a thermoplastic material such as polyolefin, typically polypropylene, the crystallinity of said plastic composition increases due to its thermal insulating properties, which in turn increases Stiffness of cellular foamed plastic compositions. Expansion of the molten plastic composition between the first and second skin layers by foaming also provides an article with good thermal insulation.

Also, because the entire container can be made from a single layer of recyclable material (ie, no layers of different materials that need to be separated), the container is easier to recycle than commonly used plastic-lined paper cups. While a label or outer coating (film or sleeve) is added to the container during manufacture, this could also be the same material that forms the container itself. For example, the polymer and membrane can both be formed from polypropylene.

Furthermore, when said article is injection molded in the process of the invention, there are no joints in the article through which the liquid contained therein can leak.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a cross-section of an article showing the appearance of the article at different stages of the method of the first aspect of the invention;

Figure 2A shows a cross-section through a part of the article at the end of step (d) of one embodiment of the method of the first aspect of the invention while the article is still in the mould;

Figure 2B shows the cross-section shown in Figure 2A showing the density of the molten plastic composition at different regions of the unexpanded article while the article is still in the mold;

Figure 3 shows a cross-section through the entire expanded product after opening the mold in step (e);

Figures 4A and 4B show the density of the foam at different locations during the expansion process to produce the article shown in Figure 3;

Figure 5 shows the expansion of the molten plastic composition in the article shown in Figure 3;

Figure 6 shows a cross section through a part of an article at the end of step (d) of one embodiment of the method of the second aspect of the invention, wherein the left hand side of the figure shows the article still in the mould, and the figure The right-hand side of shows the article after it has been expanded and removed from the mold;

Figure 7 shows the two first parts 116 and the three second parts 118 of the article at the end of step (d) of the second aspect of the invention, while the article is still in the mould;

Figure 8 shows a cross-section through a part of the article, while the article is still in the mould, at the end of step (d) of one embodiment of the method of the second aspect of the invention;

Figure 9 is a side view of an injection molded preform for cups formed by a method according to another embodiment of the present invention;

Figure 10 is a cross-sectional view through the sidewall of the injection molded preform of Figure 9;

Figure 11 is a bottom view of the bottom of the injection molded preform of Figure 9;

Figure 12 is a side view of a cup formed by expansion of the injection molded preform of Figure 9;

Figure 13 is a cross-section through the side wall of the cup of Figure 12;

FIG. 14 is a top view in transverse cross-section through the cup of FIG. 12 .

Referring to Figure 1, there is shown a cross-section of an article 2, such as a coffee cup, showing the appearance of the article at different stages of the method of the first aspect of the invention. In particular, the left hand side of Figure 1 shows at the end of step (d) of the method of the first aspect of the invention, while the article is still in the mould, the first solid skin 4, the second solid skin 6 and the and the molten plastic composition 8 between the second solid skin layers 4,6. Figure 1 shows an embodiment wherein the first forming chamber surface of the outer part 12 of the mold comprises corrugations, the corrugations in the first forming chamber surface having peaks and grooves in the form of sinusoidal waves (note that the first forming chamber surface A formation of grooves in the cavity surface results in corresponding peaks in the article molded therein, and vice versa). The sine wave can have many different configurations in the shape and morphology of the peaks and grooves.

The corrugations may for example be U-shaped or V-shaped and/or for any shape of peaks and troughs, the corrugations may have a repeatable or regular sequence of peaks and troughs or a non-repeatable or random sequence of peaks and ditch.

Typically, the peaks and grooves have some degree of curvature, with large radii of curvature. Also shown is the inner part 14 of the mold, which is the mold core. In such an embodiment, a first distance D ₁ and a second distance D ₂ (both measured perpendicular to a tangent to the second cavity-forming surface) each surround the area perimeter of the mold cavity (which The annular cross-section of the chamber between the outer and inner peripheral edges defining the chamber) remains constant. The _first distance D1 is the distance between the lowest point of the groove in the second forming chamber surface and the first forming chamber surface, and the _second distance D2 is the distance between the second forming chamber surface and the first forming chamber surface. The distance between the highest points of the peaks in .

As explained above, the first and second distances D ₁ , D ₂ are configured to provide a series of alternating peaks and grooves, or ridges and valleys, around the perimeter of the injected composition. These values may be constant or alternatively both the first and second distances D ₁ , D ₂ vary independently around said perimeter. In some embodiments of the invention, the first and second distances D ₁ , D ₂ are of constant value around said perimeter. In other embodiments of the invention, the _second distance D2 is of constant value around said perimeter, and the _first distance D1 is varied around said perimeter. In other embodiments of the invention, the _first distance D1 is constant around said perimeter, and the _second distance D2 varies around said perimeter. In other embodiments of the invention, the _second distance D2 is of a constant value around said perimeter, and the first distance D1 alternates between two different _first values around said perimeter. In other embodiments of the invention, both the first and second distances D ₁ , D ₂ vary independently around said perimeter.

The right-hand side of Figure 1 shows a first solid skin 4, a second solid skin 6 and the plastic composition between the first and second solid skin 4, 6, which plastics composition 10 has been expanded and expanded by foaming. solidification. On the right hand side of Figure 1, the outer part 12 of the mold has been removed from the article and the article remains on the inner part 14 or core. As can be seen, the expansion results in the formation of regions in the first solid skin 4, wherein said distance is the second distance D ₂ , which is "blown" so that the first and second solid skin 4 of the final article, The distance between 6 is substantially constant around the perimeter of the article (eg, varies by up to (±) plus or minus 2% compared to the average distance between the first and second skin layers).

At the end of step (d) of the method of both the first and second aspects of the present invention, said region (wherein the distance between the first and second forming chamber surfaces is a first distance D ₁ (hereinafter referred to as The "ridges")) will store latent heat and will be hotter than those areas where the distance between the first and _second forming chamber surfaces is a second distance D2 (hereinafter referred to as "valleys"). The ridge acts as a flow promoter during the filling phase of the injection molding process, ie step (b) in the method of the first and second aspects of the invention. The ridge will be the hottest part of the article as the injected material takes the path of least resistance. This stored latent heat causes the first solid skin 4 to be deformed by the pressure of the gases released by the blowing agent when the mold is opened. This pressure serves to draw the first solid skin 4 away from the second solid skin 6 . This first occurs at the ridges (i.e. the hottest part of the article) and the pressure of the first skin 4 is drawn away (either side of the highest point D1 _of the ridges) at the region of the angled portions of these ridges, It is then used to draw the first skin 4 away from the second skin 6 in the region adjacent to the valley. This effect (referred to as the "wedge effect") is discussed in more detail below.

Figure 2A shows a cross-section through a part of an article at the end of step (d) of one embodiment of the method of the first aspect of the invention while the article is still in the mould. As in Figure 1, a first solid skin 4, a second solid skin 6 and a molten plastic composition 8 between the first and second solid skins 4, 6 are shown. In such an embodiment, the first cavity-forming surface of the outer part 12 of the mold also comprises corrugations having peaks and grooves. However, in contrast to the embodiment shown in FIG. 1 , the first distance D ₁ varies around the area perimeter of the mold cavity which defines the annular cross-section of the cavity between its outer and inner peripheral edges. Specifically, the first distance D ₁ is at a maximum value D _1(max) (D _1(max) ) at every fourth groove of the mold cavity, and the first distance is at a maximum value at the first distance A minimum value D _1(min) (D _1(min) ) is reached at each groove in the middle between two grooves. Also, it is to be noted that the grooves of the first cavity-forming surface of the mold result in corresponding peaks in the article molded therein, and vice versa. In the embodiment shown in Figure 2A, the _second distance D2 remains constant around the perimeter of this region of the mold cavity.

Figure 2B shows the cross-section shown in Figure 2A showing the density of the molten plastic composition 8 at different regions within the unexpanded article. It can be seen from this figure that the density of the molten plastic composition 8 (before it expands by foaming between the first and second solid skins) is from between the first and second forming cavity surfaces of the mold therein. The higher density in those regions where the distance is the _second distance D2 changes to the lower density in those regions where the distance between the first and second forming chamber surfaces is the _first distance D1, the lower density region 20 is indicated by open cells 22 representing the presence of expanded porous foam 24 in the outer part 28 of the spine 30 . In the first and second solid skin layers 4, 6 themselves and in areas of small thickness 32 such as valleys 34, except for the outer parts 28 of the ridges 30, the density of the molten plastic composition 8 is very high, with minimal Foam or no foam.

In the cross-section shown in Figure 2B, while the article is in the mold, the ridges (where the first distance is D1 _(min) ) will start to cool and solidify upon opening the mold. The ridge (where the first distance is expressed as "D _1(middle) (D _1(int) )" (D _1(middle) is a value between D _1(min) and D _1(max) )) will be longer than where the th Ridges with a distance of D1 _(maximum) cool faster. The ridge where the first distance is D1 _(maximum) will therefore remain the hottest and will be the hottest area in the article when the mold is opened. Similar to the discussion above, this allows the first solid skin 4 to be deformed by the pressure of the gas released by the blowing agent at the ridges with the first distance D _{1 (maximum)} when the mold is opened. This pressure acts on the entire outer solid skin 4 , the inner solid skin 6 being supported by the mold core 14 .

This pressure acts to push the first outer solid skin 4 away from the second inner solid skin 6 . The push-off of the first and second skins 4, 6 is in the valley region, which has retained a high concentration of blowing agent. The first outer solid skin layer 4 can be further pushed away from the second inner solid skin layer 6 near the ridge where there is sufficient pressure from the remaining blowing agent (which has not expanded in the injection mould).

Figure 3 shows a fully expanded article in which a first outer solid skin 4" has been drawn along ridges (which may have first distances D _{1 (maximum)} , D _{1 (minimum)} and D _{1 (middle)} ) and these ridges Areas between both valleys with a second distance D2 (which may be the same or vary for said valleys) push away from the second inner solid skin 6 .

The expanded cellular foam has a lower density than the molten unexpanded plastic composition. As shown in Figure 4A, in the ridge 30 of the injection molded product, some cell voids 22 are formed by the expansion of the foaming agent in the large thickness region, while in the valley 34 of the injection molded product, the foaming agent expands in the small thickness region. Essentially unexpanded. As shown in Figure 4B, after opening the mold, the gas pressure remains evenly distributed for a few seconds, maintaining the force against the outer skin 4", and thus in the ridge 30 of the injection molded part, the cell voids 22 tend to pass through the regions of greater thickness. Further expansion of the remaining blowing agent increases and/or coalesces, whereas in the valley 34 of the injection molded part the expansion of the blowing agent is initiated in the region 32 of low thickness.

The result is that in the final expanded article 40 there are peripherically alternating regions of low density 42 and regions of high density 44 as shown in FIG. 4B . Low density regions 42 correspond to the locations of ridges 30 and are associated with relatively large sized cell voids 46 , while high density regions 44 correspond to the locations of valleys 34 and are associated with relatively small sized cell voids 48 . the average cell size is small, and the cell size is substantially uniform in the high density region 44 to provide a substantially uniform foam structure, while the average cell size is larger in the low density region 42, and The cell size is non-uniform to provide a non-uniform foam structure. In Figure 4B, it can be seen that the foam density is higher at the skin and lower at the center of the annular cross-section. Figure 4B also shows alternating high and low density foam, which is associated with low density in the ridges and high density in the valley regions.

FIG. 5 shows that thicker ridges 50 may have a greater number of cell voids 52 and/or larger cell voids 52 than cell voids 56 in thinner ridges 54 after injection molding when the ridges have different heights. Near valley 58, there is a high concentration of blowing agent, such as _CO2 in solution. By opening the mold, thereby leaving the injection molded article on the core, the outer skin 4 over the valley 58 expands rapidly as a result of the high blowing agent concentration, eg causing _CO to come out of solution and form gas. The tension holding the first and second skin layers 4, 6 together thus decreases as the foam density decreases, which is a result of cell void formation, and the pressure of gases released from the blowing agent in the molten plastic composition The result of applying it to the surface. The two skins are then pushed apart by the pressure exerted by the gas, and this pressure, along with the lower density of the plastic composition at region D (which reduces the ability of the plastic composition to constrain the first and second skins at this location ) thus causing the first and second skins to push apart and form a fully expanded article also at the valley (region D).

In a second aspect of the invention, the first forming chamber surface is such that the distance between the first forming chamber surface and the second forming chamber surface is between the first distance and the second around at least a first portion of the perimeter of the region. Alternating between distances, the first distance being greater than the second distance; and each first portion is located between a pair of second portions of the periphery of the region, wherein in the second portion, the first forming the chamber surface and the second The distance between the surfaces forming the chamber is a third distance that is less than the second distance. In step (d), the plastic composition between the first and second solid skins is allowed to solidify in the second portion, and the plastic composition between the first and second solid skins is allowed to solidify in the at least one first solid skin. One part remains molten. In step (e), the mold is then opened and the plastic composition between the first and second solid skin layers in the at least one first part is then expanded by foaming. This foaming is a result of the drop in pressure when the mold is opened and causes a blowing agent such as _CO2 to come out of solution which creates an expansion of the gas provided by the blowing agent. As mentioned above, opening the mold includes removing the outer parts of the mold such that the first solid skin no longer contacts the first forming chamber surface, while the second solid skin remains in contact with the second forming chamber surface.

Figure 6 shows a cross-section through a portion of an article 102, such as a coffee cup, showing the appearance of said article at various stages of the method of the second aspect of the invention. The left hand side of Figure 6 shows the first solid skin 104 in the first portion 116 of the perimeter of the region, the second solid skin 106, the molten plastic composition 108 between the first and second solid skins 104, 106, and At the end of step (d) of the method of the first aspect of the invention, while the article is still in the mould, the solidification 120 between the first and second solid skins 104, 106 in the second portion 118 of the region's periphery plastic composition. Figure 6 shows an embodiment wherein the first forming cavity surface of the outer part 112 of the mold comprises corrugations having peaks and grooves in the form of sinusoidal waves. Also shown is the inner part 114 of the mold. In such an embodiment, the first distance D ₁₀₁ and the second distance D ₁₀₂ surround the region perimeter of the mold cavity (which defines the annular cross-section of the cavity between the outer and inner peripheral edges of the cavity )keep constant. In the second portion 118, the third distance is shown as D ₁₀₃ . The distance between the first forming chamber surface and the second forming chamber surface is measured perpendicular to the tangent to the second forming chamber surface.

The right-hand side of Figure 6 shows the first solid skin 104 in the first part, the second solid skin 106 and the plastics composition between the first and second solid skins 104, 106, the plastics composition 110 having been passed through the development process. The bubble expands and solidifies. In the right hand side of Figure 6, the article has been removed from the mould. As can be seen, this expansion has resulted in valleys formed in the first solid skin 104 which "blown" such that the first solid skin 104 is a convex surface of the first portion 116 of the final article.

At the end of step (d) of the method of the second aspect of the invention, the region (hereinafter referred to as "ridge") in which the distance between the first and second forming chamber surfaces is the _first distance D1 will store latent heat , and will be hotter than those regions (hereinafter referred to as "valleys") where the distance between the first and second forming chamber surfaces is a _second distance D2, as discussed above with reference to the first aspect of the invention of.

Figure 7 shows the two first parts 116 and the three second parts 118 of the article at the end of step (d) of the second aspect of the invention, while the article is still in the mould. Distances D ₁₀₁ , D ₁₀₂ and D ₁₀₃ can be seen more clearly in this figure. In such an embodiment, the first distance D ₁₀₁ varies around a first portion 116 of the region's perimeter.

Figure 8 shows a cross-section through a part of the article at the end of step (d) of one embodiment of the method of the second aspect of the invention, while the article is still in the mould. As in Figure 6, there is shown a first solid skin 104, a second solid skin 106, and the molten plastic composition 108 between the first and second solid skins 104, 106 of the first portion, and in the second portion 118. The solidified plastic composition 120 between the first and second solid skin layers 104,106. In such an embodiment, the first cavity-forming surface of the outer part 112 of the mold also includes undulations in the first portion, the undulations having peaks and grooves. However, in contrast to the embodiment shown in FIG. 6 , the first distance D ₁₀₁ is a first portion of the perimeter around the region of the mold cavity (which defines the annular transverse direction of the cavity between the outer and inner peripheral edges of the cavity). section) changes. Specifically, the first distance D ₁₀₁ is at a maximum value D _{101 (max)} at the first chamber-surface-forming ditch adjacent to the second portion 118 and the first distance is at a maximum value D ₁₀₁ at the first distance The minimum value D _{101 (min)} is reached at the middle pair of grooves between the first _(maximum) grooves forming the chamber surface. Also, note that grooves in the first cavity-forming surface of the mold result in corresponding peaks in the article molded therein, and vice versa. In the embodiment shown in Figure 8, the second distance D ₁₀₂ remains constant around the perimeter of this region of the mold cavity.

The expansion mechanism in step (e) of the first aspect of the invention, as discussed above in relation to Figures 2A, 2B, 3, 4A, 4B and 5, is also applicable to the expansion in step (e) of the second aspect of the invention Expansion mechanism.

In both the first and second aspects of the invention, the limit for the minimum thickness of the valley (i.e. the minimum value of D which still allows the first and _second skins to be separated at the valley after opening the mould) is Controlled by the tension between the first and second solid skins 4, 6 and the gas pressure in the expanding foam structure which separates the solidified surface skins. The parameters affecting tension are:

1. The temperature of the molten plastic composition.

2. Blowing agent percentage (which is typically endothermic blowing agent, but can be exothermic)/or percentage and type of physical gas.

3. The speed of injection into the mold during step (b).

4. Injection pressure (higher pressure keeps more gas in solution and reduces premature foaming during injection).

5. Cooling time.

6. Mold temperature.

7. Cell size in the foam.

8. Additives present in molten plastic compositions.

Non-limiting examples of parameters that may be selected for each of points 1-8 above are given below. This example is purely an illustration of a particular embodiment and does not limit the entire invention.

1. The melting temperature of polypropylene is 165°C. However, chemical endothermic blowing agents generally require higher temperatures to activate the reaction. Likewise, the higher the temperature of the molten plastic composition, the smaller the _second distance D2 may be. For compositions where the polymer is polypropylene, a melting temperature of 250°C to 285°C may be used to minimize the _second distance D2. The same temperature range of 250°C-285°C can also be used to minimize the _second distance D2 when using a physical gas instead of a chemical blowing agent.

2. The blowing agent may be a chemical blowing agent or a physical blowing agent or any mixture of chemical and/or physical blowing agents. For example, the blowing agent may be a mixture of chemical blowing agents, such as a combination of endothermic and exothermic chemical blowing agents, or a combination of chemical and physical blowing agents, such as where the chemical blowing agent contributes to the nucleation gas , forming a physical blowing agent. Alternatively, the blowing agent may be a mixture of physical gases, such as a mixture of _CO2 and _N2 , optionally further combined with a chemical blowing agent. The chemical blowing agent used in the present invention is preferably a 50-60 wt% active level agent at a concentration of 2-6 wt%, based on the weight of the molten plastic composition, or an equivalent amount of a physical gas such as _CO2 or _N2 (at 2 A 60wt% active level agent at a wt% concentration will generate 1.2wt% gas in the molten plastic composition, so the amount of physical gas can be 1-2wt%). A physical gas such as nitrogen can be easily and inexpensively added at any wt% in the range of 0.1-10 wt%, such as 6 wt%; higher concentrations of physical gas tend to gradually increase the blowing agent outward against the skin. force.

3. A very fast injection rate is preferred, for example an injection rate of 50 g/s/chamber is required to ensure a filling time of less than 0.5 seconds; if the filling time is longer than this, then it will allow an increase in the solidified skin thickness, thus reducing The thickness of the layer of molten plastic composition between the first and second solid skin layers 4, 6 at the end of step (d) is reduced, and the swelling effect is reduced.

4. The cooling time in the mold before opening the mold in step (e) should also be minimized: however, this is limited by the time it takes to reduce the clamping force of the injection molding machine before opening the mold. Typically the time it takes to reduce the clamping force is 0.2-0.5 seconds; unless other specific mechanisms are used, this parameter defines the minimum time before the mold halves can begin to move away, allowing this first and the second surface begin to move away from each other.

5. The mold temperature affects the thickness of the solid surface. In order to slow down the solidification speed of the skin layer of polypropylene cup type products, the inner part of the mold is preferably at 40°C-70°C. Too high a temperature would cause deformation of the second solid skin, which would be undesirable. The outer part of the mold is preferably at 50°C - 120°C to keep the first skin soft enough to deform.

6. Cell size is preferably maximized in expanded foam: fine cell structure has greater melt strength which prevents skin layer separation. Cell size increases as the pressure of the molten plastic composition decreases as it flows into an expanded low pressure adjacent region. Larger cells have thinner skin and therefore lower melt strength. The cell size in the first and second skins should be 0-100 μm (microns), and the cell size in the expanded composition between said skins will be 50-250 μm or 100-500 μm or 250-1000 μm , or there is a void between the first and second skins.

7. Additives can be used to further influence the minimum value of the _second distance D2. For example chalk (calcium carbonate) will hold heat longer than polypropylene, and so including it will help slow down the skin setting. Mica, due to its sharp-edged platelets, will prevent the formation of air bubbles, thereby breaking the adhesion between the skins by creating voids.

As noted above, the sinusoidal configuration of peaks and grooves typically used in injection molded intermediate articles has a smooth curvature. In alternative configurations, the peaks and/or grooves may have shallow angles such as forming a "V" shape, and a small radius curvature; but such small radii will tend to prevent "pull-out" and Vertical ridges are left in the cup walls.

In some embodiments it may be desirable to have a series of ridges running vertically up the cup wall and this may avoid any stretching of the outer skin. This can be achieved by reducing the foaming agent % and/or increasing the cooling time, which will tend to reduce the effectiveness of the foaming, and thus achieve a cup that is partially foamed, and the valleys are not fully blown to the height of the peaks .

In some embodiments of the first and second aspects of the invention, in step (e), the first perimeter length remains substantially constant compared to the first perimeter length at the end of step (d). In some embodiments, the second perimeter length remains substantially constant compared to the second perimeter length at the end of step (d). In some embodiments, both the first and second perimeter lengths remain substantially constant compared to the first and second perimeter lengths at the end of step (d). By "essentially constant" in this context is meant a particular increase in peripheral length of up to 2% compared to the peripheral length at the end of step (d).

In other embodiments of the first and second aspects, in step (e) the first perimeter length is increased by up to 20%, up to 10%, or up to 5%. In certain embodiments, the first perimeter length is increased by 12-20%, optionally 8-15%, compared to the first perimeter length at the end of step (d); optionally compared to the end of step (d) 3-10% or 1-5% increase compared to the first perimeter length.

In some embodiments of the first or second aspect of the invention, the pattern may be embossed into the first solid surface layer of the article during the method, and/or the outer sleeve (which may be decorative) may be Formed on the outer surface (ie, the first solid skin) of the article during the method. The pattern and/or decoration may eg be a company logo. In such embodiments, step (e) further comprises, in addition to removing the outer part of the mould, the plastic composition between the first and second skins (in the at least one first part in the second aspect) completely inserting the article into the second mold prior to expansion, and maintaining the article in the second mold until the plastic composition between the first and second skins has solidified (in a second aspect in the at least one first portion middle). In the first aspect, the first solid skin layer of the article contacts the surface of the second mold when the plastic composition between the first and second skin layers is fully expanded. In a second aspect, the first solid skin of the article in said at least one first portion contacts the second mold surface when the plastic composition between the first and second skins in said at least one first portion is fully expanded .

When it is desired to emboss a three-dimensional pattern into the outer surface of the article, the surface of the second mold may contain the three-dimensional pattern. This pattern is then imparted to the first solid skin as it expands in the plastics composition between the first and second solid skins and is driven into contact with the second mold surface. When the plastic composition comprises polypropylene, the second mold will typically be heated to a temperature of 80-150°C to deform the outer solid skin by embossing.

When it is desired to include a label on the outer surface of the article, then at least part of the surface of the second mold may be covered by a film prior to inserting the article into the second mold. If it is desired to cover the outer surface of the article with a sleeve, the membrane may cover the entire perimeter of at least part of the surface of the second mould. For example in the final article, the sleeve may cover the entire perimeter of the article over only a portion of the height of the article (e.g. a broad band of sleeve material around the midpoint of the article height), or may cover the article over the entire height of the article The entire perimeter (except for the edge area). In the first aspect of the invention, at least part of the first solid skin layer of the article will be driven into contact with the membrane by expansion of the plastics composition between the first and second solid skin layers. In a second aspect of the invention at least part of the first solid skin of the article will be driven into contact with the membrane in said at least one first part by expansion of the plastics composition between the first and second solid skin. The first solid skin may also contact the membrane in the at least one second portion. In both aspects, the outer surface of the article (the first solid skin) is driven into contact with the membrane by expansion of the plastic composition between the first and second skins of the article. Likewise, the surface of the second mold may include a three-dimensional pattern, as described above. The membrane may contain plastic and/or paper. However, polypropylene (eg oriented polypropylene) is preferred because it is compatible with recycling. Foamed plastics such as polypropylene may also be used as the membrane to provide increased insulation to the article and to provide a more tactile surface to grip the article. A label can typically be placed in the mold cavity and driven into the corrugations with the injected plastic, and the label will then conform to the contours of the outer skin.

In those embodiments wherein the plastic composition between the first and second skins is fully expanded, the article is inserted into the second mold, the second skin of the article remains in contact with the second cavity-forming surface of the initial mold Contacting and moving the second mold to place on the first surface of the article. The second mold can be moved by robotic means such as a robotic arm. When the plastic composition between the first and second skins is fully expanded and the first solid skin is in contact with the second mold surface (or membrane, which covers at least part of the surface of the second mold), the article It can then be released from and retained in the second forming cavity surface of the initial mold. This second mold can then be moved by robotic means to acquire the articles for stacking.

In any embodiment of any of the above aspects of the present invention, the polymer of the plastic composition may comprise a polyolefin or a blend of polyolefins, optionally polyethylene or polypropylene; or polyester, optionally polyethylene terephthalate or polybutylene terephthalate; or polylactic acid. In one embodiment, the polymer comprises polypropylene. Especially preferred is polypropylene having a melt flow index (MFI) of 10-120. The melt flow index of the polymer can be measured according to ASTM D1238.

Blowing agents (which may be used in any embodiment of any of the above-mentioned aspects of the invention) include chemical blowing agents (which decompose under the conditions of the process, thus releasing gas into the molten plastic composition which may subsequently expansion when pressure is released on the plastic composition, for example when opening a mould, which causes the plastic composition to foam and expand). Examples of such chemical blowing agents include (from Clariant) and (from Trexel). The blowing agents are typically endothermic, but exothermic blowing agents can also be used. Alternatively, the blowing agent may be a physical blowing agent in gaseous form dissolved in the molten plastic composition. Such gases may contain, for example, carbon dioxide or nitrogen. The gas may optionally further comprise a fragrance composition (ie perfume) which remains present in the polymer material after expansion to enhance the consumer experience. The blowing agent may be a chemical blowing agent or a physical blowing agent or any mixture of chemical and/or physical blowing agents. For example, the blowing agent may be a mixture of chemical blowing agents, such as a combination of endothermic and exothermic chemical blowing agents, or a combination of chemical and physical blowing agents, such as where the chemical blowing agent contributes to the nucleation gas , forming a physical blowing agent. Alternatively, the blowing agent may be a mixture of physical gases, such as a mixture of _CO2 and _N2 , optionally further combined with a chemical blowing agent.

When using carbon dioxide as a blowing agent, the _CO2 gas is generated by the blowing agent in the extruder of the injection molding machine, and the _CO2 gas then enters the solution during the injection stage (typically 300-500bar), which is attributed to This is due to the relatively high pressure applied to the material which is greater than that required to drive _CO2 into solution within a molten thermoplastic resin such as polypropylene (typically less than 100 bar). When nitrogen is used as blowing agent, this nitrogen does not go into solution in molten polypropylene because nitrogen requires more than 3000 bar to drive it into partial solution in molten polypropylene.

In some embodiments of the first and second aspects of the invention, the molten plastic composition includes a filler. Fillers can be used to increase the strength of the product, increase its thermal conductivity, or raise the heat distortion temperature of the product. In certain embodiments, the filler is chalk or calcium carbonate.

In the first and second aspects of the invention, the article may be a cup or container, such as a coffee cup or a container suitable for warming soup in the microwave. The article may be disposable.

Another embodiment of a hollow container produced in accordance with the present invention is further described below with reference to Figures 9-14. In such an embodiment, a coffee cup, ie a cup suitable for holding a hot beverage such as coffee, is made according to the invention. In this embodiment, the coffee mug has a capacity of 16 fluid ounces. However, the hollow container can be used or shaped and dimensioned for further use as a container for food.

Initially in accordance with the present invention, as shown in Figures 9-11, a cup-shaped preform 200 is injection molded from a thermoplastic resin containing a blowing agent, in this example polypropylene and carbon dioxide ( _CO2 ) blowing agent. In preform 200, the polypropylene comprises unfoamed regions in which carbon dioxide (CO ₂ ) gas is in solution in the polypropylene after the injection molding process, and expanded porous foamed regions in which carbon dioxide (CO ₂ ) The gas already comes out of the solution in polypropylene during the injection molding process) and thereby forms porous foam regions. However, any other suitable combination of blowing agent and thermoplastic resin may be used. The blowing agent forms foamed regions in the preform as a result of the local expansion of the thermoplastic resin in the low pressure regions of the injection mold.

The cup-shaped preform 200 is injection molded to have an annular leg 202 comprising an unfoamed thermoplastic resin. The above mentioned annular leg 202 is a circular bottom wall 204 as shown in detail in FIG. 11 .

The annular side wall 206 extends upwardly away from the annular leg 202 and the circular bottom wall 204 to terminate in an annular top edge 208 .

The cup-shaped preform 200 has a height of 135mm, a top edge diameter of 90mm and a bottom diameter of 55mm. The height of the annular leg 202 is approximately 2 mm. The thermoplastic material of the cup-shaped preform 200 had an unexpanded volume (ie, the material volume of the injection molded preform before further expansion to form the final cup) of 26 cm ³ . The thermoplastic material of the cup-shaped preform 200 has an average molding density of 0.9 g/cm ³ and a weight of 24 g. The average length L/thickness T ratio of the annular sidewall 206 is 180:1, where L is the length of the sidewall 206 along the height of the sidewall 206 and T is the sidewall thickness. Lower L/T ratios of less than 180:1 can be used. However, a lower L/T ratio means higher wall thickness for a given cup height and tends to increase cup weight and lower fill pressure, which allows blowing agent to come out of solution during injection.

As shown in FIG. 9 , the annular sidewall 206 includes a plurality of longitudinal ridges 210 extending radially outward from an outer surface 211 of the annular sidewall 206 . The longitudinal ridges 210 comprise alternating thick or large ridges 212 and thin or small ridges 214 . FIG. 10 is an enlarged cross-section through annular sidewall 206 . Thick ridges 212 and thin ridges 214 comprise porous foamed thermoplastic material, and between longitudinal ridges 210 are valleys 216 comprising unfoamed thermoplastic material. The width of valleys 216 in the circumferential direction around annular sidewall 206 is 0.3-1.0 mm to provide unexpanded regions (ie, valleys 216 ) between expanded regions (ie, ridges 210 ). A typical width of the valley 216 of unfoamed thermoplastic material in the peripheral direction around the annular side wall 206 is about 1 mm.

During the injection molding process, in the position of the longitudinal ridge 210, the thermoplastic material has undergone a decompression as a result of a correspondingly thick region of the mold cavity, which enables the blowing agent to come out of solution and form gas, to form expanded cellular foam in injection molds. In contrast, during the injection molding process, in the position of the valleys 216 between the longitudinal ridges 210, the thermoplastic material has been subjected to high pressure as a result of a corresponding thin area of the mold cavity, which prevents the blowing agent from coming out of solution , thereby preventing expansion of the thermoplastic material in the injection mold.

Similarly, the annular top edge 208 is formed from expanded cellular foam in the injection mold, and the annular transition region 218 between the annular top edge 208 and the upper ends of the longitudinal ridges 210 and valleys 216 is formed of unexpanded thermoplastic material, Because the annular top edge 208 is relatively thick and the annular transition region 218 is relatively thin. Additionally, the relatively thin annular leg 202 is formed from unexpanded thermoplastic material.

FIG. 11 shows a circular bottom wall 204 . The bottom wall 204 has a central gate 220 containing an injection point for injection molding. The central gate 220 is surrounded by a first annular thick section 222 . In the illustrated embodiment (where there are five primary flow directors 224 , but any suitable number may be provided) a plurality of primary flow directors 224 extend radially outward from the first annular thick section 222 . The primary flow director 224 terminates in a second annular thick section 226 . In the embodiment shown (in which there are 40 secondary flow directors 228 , but any suitable number may be provided) a plurality of secondary flow directors 228 extend radially outward from second annular thick section 226 . The secondary flow directors 228 each terminate at the lower end of a respective thin ridge 214 . The number of secondary flow directors 228 corresponds to the number of thin ridges 214 , and also corresponds to the number of thick ridges 212 , which are respectively alternately arranged between adjacent thin ridges 214 .

The first annular thick section 222, the primary flow director 224, the second annular thick section 226 and the secondary flow director 228 have a thickness such that, as explained above for the longitudinal ridge 210, these elements are formed in the injection mold. of expanded porous foam. Typically, the thickness of these elements is 0.5-1.0 mm, for example about 0.6 mm. Instead, between the primary flow directors 224 there is a first section 230 and between the secondary flow directors 228 there is a second section 232 which has a thickness such that, as explained above for the valley 216, These elements consist of unexpanded thermoplastic material. Typically, the thickness of these elements is from 0.2mm to less than 0.5mm, for example about 0.3mm.

The dimensions of the first annular thick section 222, the primary flow director 224, the second annular thick section 226 and the secondary flow director 228, i.e. thickness and width (perpendicular and parallel to the plane of the circular bottom wall 204, respectively), are selected to This allows the thermoplastic material to easily flow away from the center gate 220 during injection molding to allow easy material flow, to reduce fill pressure and facilitate rapid injection. The thickness of the first annular thick section 222, the primary flow director 224, the second annular thick section 226 and the secondary flow director 228 is set by injection molding, and the thickness of the formed expanded porous foam is smaller than that of the annular leg 202 height (typically 2mm). This ensures that the formed cup can rest firmly on a flat surface around the perimeter of the annular leg 202, and that the expanded cellular foam region in the circular bottom wall 204 does not extend under the bottom edge of the annular leg 202, and thereby Prevents the cup from standing firmly and securely on a flat surface.

In the photographs of Figures 9-11, the unexpanded areas appear translucent to the naked eye because the blowing agent ( _CO2 gas in this embodiment) remains in solution. But if the pigment is incorporated into the thermoplastic, the unexpanded areas typically appear opaque, with a solid colour. The foamed area typically appears to have a pastel color due to the white background created by the expanded cellular foam. In Figures 9-11, it should be noted that cell sizes smaller than 0.5 microns are not visible to the naked eye.

As above, injection molding forms the outer and inner solid skins 240, 242 at the outer and inner surfaces 244, 246 of the preform 200, but the cooling time in the mold is minimized so that the molten thermoplastic resin remains on the outer and inner surfaces. Between the solid skins 240,242. After injection molding, the preform 200 is removed from the outer molded element before the mold is opened and the thermoplastic resin between the inner and outer skin layers 240, 242 solidifies, as described above. Removing the preform 200 from the outer molding element reduces the pressure on the outer surface 244 of the preform 200, which allows the blowing agent in the unexpanded region of the thermoplastic material to come out of solution and form a gas to flow between the injection mold. Expanded porous foam is formed on the outside.

In an alternative embodiment, all longitudinal ridges 210 are of the same size. In another alternative embodiment, longitudinal ridges 210 and valleys 216 may have independently varying dimensions.

The resulting cup structure is shown in Figures 12-14. Cup 250 is a hollow article for use as a beverage cup and has an annular side wall 256 and a bottom wall 204 that define a central hollow chamber 270 . The cup 250 has a top edge 208 (comprising expanded porous foam) of a sidewall 256 and a bottom end 272 of the sidewall 256 . Sidewall 256 is integrally annular molded, and most preferably annular sidewall 2567, bottom wall 204, top edge 208 and bottom end 272 are integrally annularly molded. The hollow article comprises a single plastic material, optionally thermoplastic. Typically, the hollow article is a beverage cup or food container comprising a single recyclable thermoplastic material, optionally wherein the thermoplastic material is a polymer comprising a polyolefin or a blend of polyolefins, further optionally polyethylene or polypropylene; or polyester, further optionally polyethylene terephthalate or polybutylene terephthalate; or polylactic acid. Preferably the hollow article is a coffee cup which is thermally stable up to a temperature of at least 75°C.

The annular side wall 256 comprises a plastic material comprising a sandwich of inner and outer skins 254, 252 with an expanded porous foam layer 257 therebetween. The top edge 208 is separated from the upper edge of the sandwich structure by an annular ring 218 of plastics material which is unexpanded. Expanded cellular foam layer 257 includes an annular array of reinforced regions 258 extending longitudinally along sidewall 256 in a direction between top edge 208 and bottom end 272 . Reinforcement regions 258 are spaced apart from each other by an annular array of spacer regions 260 extending longitudinally along sidewall 256 in a direction between top edge 208 and bottom end 272 to provide alternating reinforcement around annular sidewall 256. region 258 and spacer region 260 . The reinforced region 258 comprises expanded cellular foam of a first density, and the spacer region 260 comprises expanded cellular foam of a second density, wherein the first density is higher than the second density. The expanded cellular foam in the reinforcement region 258 typically has a lower concentration of cellular voids than the expanded cellular foam in the spacing region 260; and/or has a lower concentration of cellular voids than the expanded cellular foam in the spacing region 260. A more uniform size distribution of the cell voids; and/or having a smaller average size of the cell voids than the expanded cellular foam in the spacer region 260 .

In the formed cup 250 , the low density expanded foam has been retained in the large and small ridges 212 , 214 that were present in the preform 200 . The valley 216 of the preform 200 expands from the valley floor (defined by the outer solid skin 240 of the valley 216) to a position higher than the adjacent major and minor ridges 212,214. Surprisingly, however, a higher density foam was produced between the large and small ridges 212, which is believed to be of high density because no foam expansion occurred in the valleys 216 during the pre-forming process.

In the circular bottom wall 204 of the preform, the structure remains substantially in the final cup bottom, although there may be some small expansion in the front unexpanded area. The annular transition region 218 between the annular top edge 208 and the upper ends of the longitudinal ridge 210 and valley 216 remains composed of the unexpanded thermoplastic material in the cup 250 .

As shown particularly in FIG. 13 , the formed cup has a slightly contoured outer peripheral surface 252 for side walls 256 and a substantially smooth inner peripheral surface 254 . Sidewall 256 contains expanded porous foam 257 . Outer peripheral surface 252 has a slightly higher surface at the location of valley 216 of preform 200 . However, optimization of the blowing agent concentration, cooling time, and preform temperature upon removal from the injection mold can be controlled to achieve a substantially smooth outer peripheral surface 252 .

5, the foam density varies around the perimeter of sidewall 256, alternating between regions of relatively high density 258, which constitute regions of reinforcement 258, which correspond to the location of valleys 216 of preform 200, and regions of relatively low density. Density regions 260 , constituting spacing regions 260 , which correspond to the position of the longitudinal ridges 210 of the preform 200 . The alternating reinforcement regions 258 and spacing regions 260 around annular sidewall 256 provide that each reinforcement region 258 is located between opposing spacing regions 260 , and each spacing region 260 is located between opposing reinforcement regions 258 .

The low density regions 260 comprise a first low density region 260a (corresponding to the location of the large longitudinal ridges 212 of the preform 200) and a second low density region 260b (corresponding to the location of the small longitudinal ridges 214 of the preform 200), and The foam density in the second low density region 260b is slightly higher than in the first low density region 260a , but in each case the foam density is lower than in the relatively high density region 258 , which corresponds to the location of the valley 216 . In an alternative embodiment where the longitudinal ridges 210 are of the same size, the low density regions 260 are of the same size and properties and alternate with the high density regions 258 .

The spacer region 260 includes first and second spacer regions 260a, 260b, the width of the first spacer region 260a in the peripheral direction around the annular sidewall 256 is greater than that of the second spacer region 260b. The first and second spaced regions 260a, 260b comprise expanded porous foam, and the expanded porous foam of the first spaced region 260a has a lower density than the expanded porous foam of the second spaced region 260b. The first and second spacing regions 260 a , 260 b alternate around the annular sidewall 256 . Alternating the reinforcement region 258 and first and second spacer regions 260a, 260b around the annular sidewall provides a repeating sequence of reinforcement region 258, first spacer region 260a, reinforcement region 258 and second spacer region 260b.

The width of the reinforcement region 258 in the peripheral direction around the annular side wall is 0.5-3 mm, optionally 0.75-2 mm. The width of the spacing region 260 in the circumferential direction around the annular sidewall is 0.5-10 mm, optionally 0.5-4 mm, further optionally 0.75-3 mm. The thickness of the side wall is 0.5-4 mm, optionally 1-3 mm.

As mentioned above, in the circular bottom wall 204 of the preform, the structure remains substantially in the final cup bottom, although there will be some small expansion of the previously unexpanded areas. So in the hollow article or cup 250, the bottom wall 204 comprises a central gate region 280, a first annular ring 282 of expanded porous foam surrounding the gate region 280, and an expanded porous foam extending radially outward toward the side wall 256. A first radial element 284 of foam. The first radial elements 284 are separated from each other by a first section 286 of unexpanded plastic material. The bottom wall 204 further comprises a second annular ring 288 of expanded porous foam surrounding and connected to a radially outer end 290 of the first plurality of radial elements 284, and a second plurality of radial elements 292 of expanded porous foam. , which extend radially outwardly toward sidewall 256 . The second radial elements 292 are separated from each other by a second section 294 of unexpanded plastic material. The radially outer ends 296 of the plurality of second radial elements 294 of expanded cellular foam are connected to the side wall 256 , in particular to a respective spacer region 260 , typically a first spacer region 260 a , in the side wall 256 .

A typical thickness of the unexpanded plastic material in the bottom wall 204 is 0.25-0.75 mm, optionally 0.25-0.5 mm. The expanded cellular foam of plastics material in the bottom wall 204 typically has a thickness of 0.5-1.75 mm, optionally 0.5-1.25 mm.

The hollow article 250 further includes at least one leg 298 extending downwardly from the bottom end 272 of the side wall 256 and defining at least one lower surface 300 positioned lower than the bottom surface 302 of the bottom wall 204 . Preferably, the at least one leg 298 comprises a single annular leg 298 having a single annular lower surface 300 and comprising unexpanded plastic material integrally molded with the side walls 256 and bottom wall 204 and having a height of 1.5- 4mm, optionally 1.75-3mm.

Alternating and repeating foam densities around cup 250 are shown in FIGS. 13 and 14 . The resulting foam structure of alternating high/low density expanded cellular foam regions around the perimeter of the cup provides a high loading capacity of the cup when loaded in the longitudinal direction; The resulting fractures have high resistance. Alternating high/low density expanded cellular foam regions extend longitudinally along the sidewalls such that the high density regions 258 constitute longitudinal reinforcing ridges separated by longitudinal low density foam regions 260a, 260b. This longitudinal crush strength is essentially twice that of a foam sidewall of comparable thickness but with a constant foam density around the periphery of the cup. The cup also has a very high flexural stiffness and a very high hoop stiffness in the sidewall, which is evident in comparison with cup sidewalls of unfoamed thermoplastic material of corresponding structural properties This is achieved by reducing the mass of thermoplastic material. In short, the foamed cup of the present invention can provide high structural strength to the sidewall using a minimum amount of thermoplastic material in the cup, which can be formed from a single thermoplastic material.

The stiffness of cups formed using the preferred embodiments of the present invention is far superior to any other limited use cups currently on the market. The cup typically comprises a thermoplastic polymer, which can have a high degree of crystallinity, and thus high thermal stability, in both the foamed and unfoamed parts. Preferred cups of the present invention are thus dishwasher safe and microwave safe, and will exhibit unlimited re-use.

The present invention can provide high-strength hollow articles having a high volume-to-weight ratio. For example, the ratio of the volume cm ³ of the central hollow chamber to the mass g of the hollow product is 2-3.

The expanded volume of the thermoplastic material of the cup 250 of the illustrated embodiment (i.e., the material volume of the final cup) is 55.6 cm ³ , and compared to the preform (whose unexpanded volume is 26 cm ³ ), this represents the Expansion of about 110% between the formed bodies, which occurs outside the injection mold due to: significant outward expansion of the perimeter of the valley 216, and outward expansion of the lowered perimeter of the longitudinal ridge 210 to form the hair of the cup 250. Bubble sidewall 256.

Typically, the change in volume from the intermediate pre-formed cup to the final fully expanded cup is about 2.1:1, but this ratio can easily be varied from 1.5:1 to 3:1 through design and processing control.

In the embodiment shown in Figures 9-14, a coffee cup is typically formed. However, the invention can be used to produce hollow containers having a height as low as about 10 mm, for example forming trays, or wide mouth containers such as pots, for example for hot or cold food ingredients, such as takeaway food, frozen food or ready-to-eat food .

Various modifications to the illustrated embodiments will be apparent to those skilled in the art and are intended to be included within the scope of the invention.

Claims (75)

1. A method of forming an article, the method comprising: (a) providing a mold having an outer part having a first cavity-forming surface and an inner part having a second cavity-forming surface; (b) closing the mold thereby defining a cavity between the first and second cavity-forming surfaces, wherein at least one region of the cavity defines the cavity between the outer and inner peripheral edges of the cavity An annular cross-section, the first forming chamber surface is such that the distance between the first forming chamber surface and the second forming chamber surface alternates between a first distance and a second distance around at least part of the perimeter of the region , the first distance is greater than the second distance; (c) injecting a molten plastic composition comprising a polymer and a blowing agent into the cavity; (d) causing the plastic composition to form a first solid skin and a second solid skin in the at least one region, the first solid skin being adjacent to and in contact with the first forming chamber surface, and having a first perimeter length , the second solid skin is adjacent to and in contact with the second forming chamber surface, and has a second perimeter length, wherein the plastic composition remains molten between the first and second solid skins to form respectively: wherein the The distance between the first forming chamber surface and the second forming chamber surface alternates between the first distance and the second distance, alternating the first and second thicknesses of the plastic composition, the first and second thicknesses each comprising first and second skins and a molten plastic composition therebetween; (e) before the plastic composition between the first and second solid skins solidifies, the mold is opened, thereby allowing the plastic composition between the first and second solid skins, and the plastic composition to alternate molten plastic compositions of first and second thicknesses, expanded by foaming, wherein said opening comprises removing the outer part of the mold such that the first solid skin no longer contacts the first forming chamber surface, Instead, the second solid skin remains in contact with the second forming chamber surface. 2. The method of claim 1, wherein the second solid skin remains in contact with the second forming chamber surface until the plastic composition between the first and second solid skins is fully expanded. 3. The method of claim 1 or claim 2, wherein step (e) further comprises, after removing the outer part of the mold, before the plastic composition between the first and second skins is fully expanded, the inserting the article into the second mold, and maintaining the article in the second mold until the plastic composition between the first and second skins solidifies, wherein when the plastic composition between the first and second skins When the article is fully expanded, the first solid skin layer of the article contacts the surface of the second mold. 4. The method of claim 3, further comprising covering at least part of the surface of the second mold with a film before inserting the article into the second mold; Wherein at least a portion of the first solid skin layer of the article contacts the membrane when the plastic composition between the first and second skin layers is fully expanded. 5. The method of any preceding claim, wherein the first surface comprises corrugations having peaks and grooves, optionally wherein (i) the corrugations are U-shaped or V-shaped, and/or (ii ) The corrugation has a repeatable or regular sequence of peaks and grooves, or a non-repeatable or random sequence of peaks and grooves. 6. The method of forming an article of claim 1, wherein in step (b), each first portion is located between a pair of second portions at the periphery of the region in which the first forming chamber surface and the distance between the second chamber-forming surface is a third distance, which is less than the second distance; step (d) also causes the plastic composition between the first and second solid skins to be in said second portion solidified while the plastic composition between the first and second solid skins remains molten in the at least one first part; and in step (e), the first and second parts in the at least one first part The mold is opened before the plastics composition between the solid skins solidifies, thus allowing the plastics composition between the first and second solid skins in said at least one first part to expand by foaming. 7. The method of claim 6, wherein the second solid skin remains in contact with the second forming chamber surface until the plastic composition between the first and second solid skins in the at least one first portion is completely swell. 8. The method of claim 6 or claim 7, wherein around said at least one first portion of the area periphery, the first surface comprises corrugations, the corrugations having peaks and grooves, optionally wherein (i) the corrugations are U -shaped or V-shaped, and/or (ii) the corrugations have a repeatable or regular sequence of peaks and grooves, or a non-repeatable or random sequence of peaks and grooves. 9. The method of any preceding claim, wherein in step (e) the first perimeter length remains substantially constant compared to the first perimeter length at the end of step (d). 10. The method of claim 9, wherein in step (e) the first perimeter length is increased by up to 2% compared to the first perimeter length at the end of step (d). 11. The method of any one of claims 1-8, wherein in step (e) the first perimeter length is increased by up to 20% compared to the first perimeter length at the end of step (d). 12. The method of claim 11, wherein in step (e) the first perimeter length is increased by 12-20%, alternatively by 8-15%, compared to the first perimeter length at the end of step (d). 13. The method of claim 11, wherein in step (e), the first perimeter length is increased by up to 10% compared to the first perimeter length at the end of step (d). 14. The method of claim 13, wherein in step (e), the first perimeter length is increased by 3-10% compared to the first perimeter length at the end of step (d). 15. The method of claim 13, wherein in step (e) the first perimeter length is increased by up to 5% compared to the first perimeter length at the end of step (d). 16. The method of claim 15, wherein in step (e), the first perimeter length is increased by 1-5% compared to the first perimeter length at the end of step (d). 17. The method of any preceding claim, wherein in step (e) the second perimeter length remains substantially constant compared to the second perimeter length at the end of step (d). 18. The method of claim 17, wherein in step (e) the second perimeter length is increased by up to 2% compared to the second perimeter length at the end of step (d). 19. The method of any preceding claim, wherein the distance between the first forming chamber surface and the second forming chamber surface is measured perpendicular to a tangent to the second forming chamber surface. 20. The method of claim 5 or claim 8, or any claim dependent thereon, wherein the ripple is in the form of a sine wave. 21. The method of claim 5, claim 8 or claim 20 or any claim dependent thereon, wherein the first distance is the distance between the second forming chamber surface and the lowest point of the trench, and the second The second distance is the distance between the second forming chamber surface and the highest point of the peak. 22. The method of any preceding claim, wherein the second distance remains constant around the perimeter of the region. 23. The method of any preceding claim, wherein the first distance remains constant around the perimeter of the region. 24. The method of any one of claims 1-23, wherein the first distance and/or the second distance vary around the perimeter of the region. 25. The method of claim 24, wherein the first distance varies around the perimeter of the region and reaches a maximum at every nth trench around the perimeter of the region, where n is at least 2 and is an integer. 26. The method of claim 25, wherein the first distance reaches a minimum at each trench or pair of trenches midway between adjacent nth trenches around the perimeter of the region. 27. The method of claim 25 or 26, wherein n is 2-20, optionally 2-10, further optionally 2-5, further optionally 3-4. 28. The method of claim 24, wherein the first distance varies around the region perimeter, and each first portion comprises n grooves at which the first distance is at a maximum, where n is at least 1 and is an integer , optionally wherein n is 1-20, optionally 1-10, further optionally 1-5. 29. The method of claim 28, wherein in said at least one first portion, the first distance is at a maximum at each trench adjacent to a second portion. 30. The method of claim 29, wherein n is at least 2 and is an integer, optionally wherein n is 2-20, optionally 2-10, further optionally 2-5. 31. The method of any one of claims 28-30, wherein the first distance reaches a minimum at each groove or pair of grooves between adjacent grooves for which the first distance is a maximum middle. 32. The method of claim 6 or any claim dependent thereon, wherein step (e) further comprises after removing the outer part of the mould, between the first and second skins in the at least one first part Before the plastic composition between is fully expanded, insert this article in the second mold, and keep this article in this second mold, until the gap between the first and second skins in the at least one first part The plastic composition solidifies, wherein when the plastic composition between the first and second skins in the at least one first part is fully expanded, the first solid skin of the article in the at least one first part and the second mold surface contact. 33. The method of claim 32, further comprising covering at least part of the surface of the second mold with a film prior to inserting the article into the second mold, wherein at least part of the first solid skin of the article in said at least one first portion is in contact with said membrane when the plastic composition between said first and second skins is fully expanded. 34. The method of claim 3 or any claim dependent thereon, claim 32 or claim 33, wherein the surface of the second mold comprises a three-dimensional pattern applied to the first surface layer. 35. The method of claim 4 or any claim dependent thereon, or claim 33 or any claim dependent thereon, wherein the membrane covers the entire perimeter of at least part of the surface of the second mould. 36. The method of claim 4 or any claim dependent thereon, or claim 33 or any claim dependent thereon, wherein the membrane is a polypropylene membrane. 37. The method of claim 36, wherein the polypropylene is oriented or biaxially oriented polypropylene. 38. The method of claim 4 or any claim dependent thereon, or claim 33 or any claim dependent thereon, wherein the membrane is a foamed membrane. 39. The method of any preceding claim, wherein the polymer comprises a polyolefin or a blend of polyolefins, optionally polyethylene or polypropylene; or polyester, optionally polyethylene terephthalate glycol ester or polybutylene terephthalate; or polylactic acid. 40. The method of claim 39, wherein the polymer comprises polypropylene having a melt flow index of 10-120. 41. The method of any preceding claim, wherein the blowing agent is a chemical blowing agent. 42. The method of any one of claims 1-41, wherein the blowing agent is a gas dissolved in the molten plastic composition, optionally wherein the gas comprises carbon dioxide or nitrogen, further optionally wherein the gas further comprises Fragrance composition. 43. The method of any preceding claim, wherein the molten plastic composition further comprises a filler. 44. The method of claim 43, wherein the filler comprises calcium carbonate or chalk. 45. The method of any preceding claim, wherein the article is a cup or container. 46. A hollow article for use as a beverage cup or as a container, the hollow article having annular side walls and a bottom wall defining a central hollow chamber, a top edge of the side wall and a bottom end of the side wall, wherein the annular side wall comprising a plastic material comprised of a sandwich structure of inner and outer skins with an expanded cellular foam layer therebetween, wherein the expanded cellular foam layer comprises an annular array of reinforced regions along the sidewall at the top extending longitudinally in a direction between the edge and the bottom end, the reinforced regions being separated from each other by an annular array of spacer regions extending longitudinally along the sidewall in a direction between the top edge and the bottom end, to provide alternating reinforced regions and spaced regions around the annular sidewall, wherein the reinforced regions comprise expanded first density cellular foam and the spaced regions comprise expanded second density porous foam, wherein the first density is higher than the second density density. 47. The hollow article of claim 46, wherein the expanded cellular foam in the reinforced region has a lower cell void concentration than the expanded cellular foam in the spaced region. 48. A hollow article according to claim 46 or claim 47, wherein the expanded cellular foam in the reinforced region has a more uniform size distribution of cell voids than the expanded cellular foam in the spaced region. 49. The hollow article according to any one of claims 46-48, wherein the expanded cellular foam in the reinforced region has a smaller average cell void size than the expanded cellular foam of the spaced region. 50. The hollow article according to any one of claims 46-49, wherein the alternating reinforcement regions and spacer regions around the annular sidewall provide that each reinforcement region is located between opposite spacer regions, and each spacer region is located between opposite spacer regions. between enhanced regions. 51. The hollow article according to any one of claims 46-50, wherein the spacer region comprises first and second spacer regions, the first spacer region having a greater spacing than the second spacer in a peripheral direction around the annular sidewall. The wider width of the region. 52. The hollow article according to claim 51 , wherein the first and second spaced regions comprise expanded porous foam, and the expanded porous foam of the first spaced region has a lower density than the expanded porous foam of the second spaced region. density of. 53. A hollow article according to claim 51 or claim 52, wherein the first and second spaced regions alternate around the annular side wall. 54. The hollow article of claim 53, wherein alternating reinforcement regions and first and second spacer regions around the annular sidewall provide a repeating sequence of reinforcement regions, first spacer regions, reinforcement regions and second spacer regions. 55. Hollow article according to any one of claims 46-54, wherein the width of the reinforced region is 0.5-3 mm, optionally 0.75-2 mm, in the peripheral direction around the annular side wall. 56. The hollow article according to any one of claims 46-55, wherein in the peripheral direction around the annular side wall, the width of the spacer region is 0.5-10 mm, optionally 0.5-4 mm, further optionally 0.75-3 mm . 57. A hollow article according to any one of claims 46-56, wherein the thickness of the side wall is 0.5-4 mm, optionally 1-3 mm. 58. A hollow article according to any one of claims 46-57, wherein the side wall is integrally ring molded. 59. A hollow article according to any claim 58, wherein the annular side wall, bottom wall, top edge and bottom end are integrally annular molded. 60. A hollow article according to any one of claims 46-59, wherein the hollow article consists of a single plastic material, optionally a thermoplastic material. 61. A hollow article according to any one of claims 46-60, wherein the top edge comprises an annular ring of expanded porous foam. 62. A hollow article according to claim 61, wherein the top edge is separated from the upper edge of the sandwich structure by an annular ring of unexpanded plastics material. 63. The hollow article according to any one of claims 46-62, wherein the bottom wall comprises a central gate area, a first annular ring of expanded porous foam surrounding the gate area, and radially outwardly extending towards the side walls. A plurality of first radial elements of expanded cellular foam separated from one another by a first section of unexpanded plastic material. 64. The hollow article according to claim 63, wherein the bottom wall further comprises a second annular ring of expanded porous foam surrounding and connected to the radially outer ends of the plurality of first radial elements, and toward A plurality of second radial elements of expanded porous foam with sidewalls extending radially outward, the second radial elements being separated from each other by a second section of unexpanded plastic material, the expanded porous foam The radially outer ends of the plurality of second radial elements are connected to the side wall. 65. The hollow article of claim 64, wherein the radially outer ends of each of the plurality of second radial elements of expanded cellular foam are attached to respective spaced regions in the sidewall. 66. A hollow article according to any one of claims 63-65, wherein the thickness of the unexpanded plastics material in the bottom wall is 0.25-0.75 mm, optionally 0.25-0.5 mm. 67. Hollow article according to any one of claims 63-66, wherein the thickness of the expanded porous foam of plastics material in the bottom wall is 0.5-1.75 mm, optionally 0.5-1.25 mm. 68. The hollow article according to any one of claims 46-67, further comprising at least one leg extending downwardly from the bottom end of the side wall and defining at least one lower surface, the lower surface being positioned lower than the bottom wall. bottom surface. 69. The hollow article of claim 68, wherein the at least one leg comprises a single annular leg having a single annular lower surface. 70. A hollow article according to claim 68 or claim 69, wherein the at least one leg comprises unexpanded plastics material. 71. The hollow article according to any one of claims 68-70, wherein the at least one leg is integrally molded with the side wall and the bottom wall. 72. Hollow article according to any one of claims 68-71, wherein the height of the at least one leg is 1.5-4mm, optionally 1.75-3mm. 73. A hollow article according to any one of claims 46-72, which is a drinking cup or a food container, consisting of a single recyclable thermoplastic material, optionally wherein the thermoplastic material is a polymer comprising a polyolefin or a blend of polyolefins, further optionally polyethylene or polypropylene; or polyester, further optionally polyethylene terephthalate or polybutylene terephthalate; or poly lactic acid. 74. A hollow article according to any one of claims 46-73 which is a coffee cup which is thermally stable up to a temperature of at least 75°C. 75. The hollow article according to any one of claims 46-74, wherein the ratio of the volume of the central hollow chamber to the mass of the hollow article is ^2-3 , wherein the volume of the central hollow chamber is in cm , and The mass of the hollow article is measured in g.